Fabrication and Characterization of Perovskite LED Devices

The ITO glasses were cleaned with Triton X-100, isopropanol, and deionized water with ultrasonic cleaning for 30 min each. Then the glasses were exposed under O₂ plasma for a quarter of an hour. After that, NiO_x precursor was spin-coated the substrates and baked under 300 °C for 45 min covered with a big glass dish. Then, poly-TPD (6 mg mL⁻¹ in chlorobenzene) layers and PVK (4 mg mL⁻¹ in xylene) was spin-coated onto the NiO_x at 3000 rpm and annealed on a hot plate for 20 min at 130 °C in a glovebox. The precursor was spin-coated onto the PVK substrate at 3000 rpm for 1 min, and annealed at 80 °C for 5 min. Last, 40 nm of TPBi, 1.2 nm of LiF, and Al (120 nm) electrodes were deposited under a based vacuum of ~7 × 10⁻⁷ torr.
The current density, luminance, and EQE values were tested by a Keithley 2612B and an integrating sphere (FOIS-1) with a QE Pro650 spectrometer (SpectrumTEQ-EL system). The EQE of LED can be defined as $\mathrm{EQE}=\frac{\mathrm{emitted}\mathrm{photons}\mathrm{out}\mathrm{LED/second}}{\mathrm{injected}\mathrm{electrons/second}}$ . The counts of photons per second are collected by an integrating sphere and a fiber spectrometer and the counts of electrons are collected with Keithley 2612B source meter. The LED devices were tested on top of the integrating sphere, and only forward light emission could be collected, which is consistent with the standard OLED characterization method. All the device test processes were performed in the N₂-filled glovebox. The EL data of the 100 mm² devices were measured by PR-655 spectrometer with a Keithley 2400.